What does SET XACT_ABORT ON do in SQL

In SQL, the SET XACT\_ABORT ON statement is used to enable or disable the automatic termination of transactions that encounter errors or take too long to complete. When this statement is enabled, any transaction that encounters an error or takes longer than a specified time will be automatically rolled back, and the user will receive an error message indicating what went wrong.

The XACT\_ABORT ON statement can be used in two ways:

1. SET XACT\_ABORT ON FOR SESSION - This statement enables automatic transaction termination for all transactions within a session. It is useful when you want to ensure that all transactions are rolled back if they encounter an error or take too long to complete.

2. SET XACT\_ABORT ON FOR SUBSESSION - This statement enables automatic transaction termination only for transactions within the current subsession. It is useful when you want to enable automatic transaction termination for a specific set of transactions, but not for all transactions within a session.

Here's an example of how to use the SET XACT\_ABORT ON FOR SESSION statement:

sql
SET XACT_ABORT ON FOR SESSION;
BEGIN TRANSACTION;
-- This transaction will take too long to complete
DECLARE @i INT = 1;
WHILE @i <= 1000000
BEGIN
    -- Do some work here
    SET NOCOUNT ON;
END
COMMIT;

In this example, the transaction is set to take too long to complete by using a while loop that iterates 1 million times. If the XACT\_ABORT ON FOR SESSION statement is enabled, the transaction will be automatically rolled back when it takes longer than the specified time (which is not shown in this example).

Here's an example of how to use the SET XACT\_ABORT ON FOR SUBSESSION statement:

sql
SET XACT_ABORT ON FOR SUBSESSION;
BEGIN TRANSACTION;
-- This transaction will take too long to complete
DECLARE @i INT = 1;
WHILE @i <= 1000000
BEGIN
    -- Do some work here
    SET NOCOUNT ON;
END
COMMIT;

In this example, the XACT\_ABORT ON FOR SUBSESSION statement is used to enable automatic transaction termination only for the current subsession. If the transaction takes too long to complete, it will be automatically rolled back.

It's important to note that the time limit for automatic transaction termination can be set using the SP\_CONFIG system stored procedure. For example, you can use the following command to set the maximum amount of time a transaction can take before it is automatically rolled back:

sql
EXEC sp_config 'Maximum Transaction Time (in seconds)', 300;

This will set the maximum amount of time a transaction can take to 300 seconds. If a transaction takes longer than this time limit, it will be automatically rolled back.

In addition to enabling automatic transaction termination, the SET XACT\_ABORT ON statement can also be used to manually roll back transactions that have encountered errors or taken too long to complete. To manually roll back a transaction, you can use the ROLLBACK TRANSACTION command followed by the name of the transaction:

sql
ROLLBACK TRANSACTION MyTransaction;

This will roll back the transaction named "MyTransaction" and undo any changes that were made during the transaction.

In conclusion, the SET XACT\_ABORT ON statement is a useful tool for ensuring that transactions are rolled back automatically if they encounter errors or take too long to complete. By enabling automatic transaction termination, you can help prevent data corruption and ensure that your database remains in a consistent state. Additionally, the SP\_CONFIG system stored procedure allows you to set the maximum amount of time a transaction can take before it is automatically rolled back, giving you greater control over how transactions are managed.